A mobile communication system in 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) aims for an architecture as shown in FIG. 7. It is an object of this architecture to build a system that can realize shortening of transmission delay in a control plane and a user plane, and in which data transfer with higher throughput, for example, than existing systems can be realized.
An operator provides a service to a user in this system, and charges a fee; one charging method therefor that can be considered is to charge only for the number of packets that the user used.
In order to charge for the number of packets that the user used, it is necessary to count the number of packets that the user used. A method of doing this count is to count only the amount of packets that a network has successfully received, in an uplink case, and to count only the amount of packets that a user has successfully received, in a downlink case, and to charge for the number of counted uplink and downlink packets only.
With regard to counting the number of packets, since the number of packets successfully received is counted in the uplink case, normally CN (Core Network) Nodes of the network perform the count.
In the downlink case, packets transmitted by the network are not necessarily completely delivered to UE (User Equipment), due to radio wave state. For example, packet #1, packet #2, and packet #3 are transmitted from a network to the UE; packet #1 and packet #2 are successfully received by the UE, but packet #3 is not successfully received by the UE. In view of this type of situation, counting the amount of packets successfully received is considered at the UE. That is, counting is performed by a self-assessment of the UE.
However, if the UE performs the count, a case may be considered where, for example, a malicious UE or an altered UE reports to the network a number less than the actual number successfully received. In order to prevent this, the number of downlink packets is usually counted by the network. In this mechanism, for downlink packets transmitted from the network to the UE, a confirmation is made that a transmission confirmation (Acknowledge) from the UE has been received by the network, and the number of downlink packets is counted.
A function of this transmission confirmation is held by an entity called RLC (Radio Link Control) at an eNode B of the network, so that the number of successfully transmitted downlink packets is counted by the eNode B. This situation is shown in FIG. 9. Furthermore, “reporting the number counted to a CN Node”, which reports to the CN Node, from the eNode B shown in FIG. 9, is normally performed when communication between the eNode B and the UE is ended and communication connection is cut.
On the other hand, in this LTE architecture, when an area covering one eNode B is small (for example, an urban area), there is a possibility that handover signals from the eNode B to the CN Node will increase enormously, due to UE movement between eNode Bs. In such a case, an excessive signal load is given to the CN.
In order to suppress handover signal load on the CN Node, exchanging of handover signals directly between a mobile source base station (Source eNode B) and a mobile target base station (Target eNode B) is devised. Furthermore, with a handover signal (Handover Request message of FIG. 8) received by the Target eNode B from the Source eNode B, if the handover is successful, that is, if confirmation of the Target eNode B establishing a communication connection with the UE is completed, the handover procedure is completed by the Target eNode B only transmitting one Handover Complete signal to the CN Node.
Here, the Handover Complete signal name is an example, and there are other names such as, for example, Path Switch, Binding Update, and the like, all of which have the same meaning.
The CN Node that receives this Handover Complete signal switches a UE directed path from the Source eNode B to the Target eNode B. In this way, it is possible to reduce the signal load and processing load due to handover at the CN Node.
In this handover method, information on the number of downlink packets counted before the mobile source eNode B performs handover, that is, “reporting the number counted to the CN Node” of FIG. 9 must be reported to the CN Node. Otherwise, the number of packets counted by the mobile source eNode B cannot be charged for.
In a conventional handover method (shown in FIG. 10), with a disconnect signal (Iu Release Command) from the CN Node as a trigger, the number counted by the mobile source eNode B is reported to the CN Node by the mobile source eNode B. Specifically, the Source eNode B reports the counting method to the CN Node by an Iu Release Complete message of FIG. 10.
Furthermore, even outside of the handover case, after ending of communication between the UE and the network, similarly to the above, with a disconnect signal (Iu Release Command) from the CN Node as a trigger, the eNode B reports the method of “reporting the number counted to the CN Node” to the CN Node by the Iu Release Complete message.
Technology related to the abovementioned mobile communication system is disclosed in the following patent documents.    [Patent Document 1]
JP Patent Kokai Publication No. JP-P2003-283510A    [Patent Document 2]
JP Patent Kokai Publication No. JP-P2007-013463A    [Patent Document 3]
JP Patent Kohyo Publication No. JP-P2001-513285A